1. Field of the Invention
The present invention relates to a bump transfer plate used for a semiconductor package and the like, a manufacturing method of the bump transfer plate, a manufacturing method of a semiconductor device with the bump transfer plate, and the semiconductor device manufactured by the method, and more specifically to a bump transfer plate with high reliability, a manufacturing method thereof, a manufacturing method of a semiconductor device with the bump transfer plate, and the semiconductor device manufactured by the method.
2. Description of Related Art
Recently, new types of semiconductor devices have been successively developed to meet the demands of high functionality, miniaturization and lightening, and the speeding up of electronic equipment. For example, size reduction and width reduction are achieved by using bumps of solder or the like for external terminals in a semiconductor device that adopts a package such as Ball-Grid-Array or Chip-Size-Package.
Such bumps are used to electrically connect an electrode formed in a semiconductor element with a wiring pattern of a package to each other, and mount the semiconductor element on a printed board. A transfer method, in which bumps are formed on electrodes formed in a semiconductor element by transfer can be mentioned as one of the methods of forming bumps. In the transfer method, bump formation materials such as solder are first formed on a base so as to meet the arrangement of the electrodes of a semiconductor element. Thereafter, the bump formation materials and the electrodes of the semiconductor element are caused to coincide with each other to adjust each position, and the base and the semiconductor element are overlapped. The bump formation materials are transferred to the electrodes of the semiconductor element, and thereby bumps are formed on the semiconductor element. FIG. 1A through FIG. 1C show a bump transfer plate for the conventional transfer method. FIG. 2A through FIG. 2E are sectional views showing the sequential steps for manufacturing the conventional bump transfer plate. FIG. 1A is a top view, FIG. 1B is a sectional view, and FIG. 1C is an enlarged view of FIG. 1B.
As shown in FIG. 1A, in a conventional bump transfer plate 121, solder bumps 122 of eutectic solder or high melting point solder are formed on a base 123 made of Al or stainless steel. The solder bumps 122 are arranged to meet the arrangement of electrodes of a semiconductor element to be connected in a later process.
When the bump transfer plate 121 is manufactured, a photo resist layer 124 is first formed on the main surface of the base 123 of FIG. 2A, as shown in FIG. 2B. Thereafter, the photo resist layer 124 is exposed with a mask of a predetermined pattern and developed, thereby forming holes 125, as shown in FIG. 2C, in order to form solder bumps in the later process. Subsequently, the holes 125 are filled with bump formation materials 126 as shown in FIG. 2D, and the photo resist layer 124 is removed as shown in FIG. 2E, thereby forming solder bumps 122. Thus, the bump transfer plate 121 is obtained.
FIG. 3A and FIG. 3B are sectional views showing the sequential steps of a conventional method for manufacturing a semiconductor device, and FIG. 4A through FIG. 4D are sectional views showing the manufacturing method of FIGS. 3A and 3B in detail.
When a semiconductor device is manufactured by the use of the bump transfer plate 121 manufactured as mentioned above, the bump transfer plate 121 is first disposed on a table 17 such that the surface on which the solder bumps 122 are disposed faces a surface on which electrodes 7 of a semiconductor element 1 are disposed, as shown in FIG. 3A and FIG. 4A. An insulating film 3 made of polyimide or the like is formed around the electrodes 7 of the semiconductor element 1. However, the insulating film 3 is not formed on the electrodes 7. Therefore, concave-shaped structures are formed by the insulating film 3 and the electrodes 7. That is, the insulating film 3 and the electrodes 7 form concave portions 8.
The electrodes 7 are then adjusted to coincide with the positions of the solder bumps 122 and is brought into contact therewith as shown in FIG. 3B and FIG. 4B. Thereafter, as shown in FIG. 4C, the solder bumps 122 are transferred onto the electrodes 7 by the reflow of the solder bumps 122, and the base 123 is removed as shown in FIG. 4D.
Another method of forming bumps on a semiconductor element according to the transfer method is disclosed in Japanese Laid-open Patent Publication No. Hei 9-148330. FIG. 5A through FIG. 5H are sectional views showing the sequential steps of the manufacturing method of this publication.
In the method disclosed in the publication, a resist layer 144 is first formed on a base 143 by means of a spin coater, as shown in FIG. 5A, and then holes 145 are formed in the resist layer 144, so that a bump transfer plate 141 is formed. Thereafter, a bump formation materials 142a are formed on the base 143 by metal plating, as shown in FIG. 5B, and the bump formation materials 142a are melted by reflow. If the wettability of the bump formation materials 142a and the base 143 is low at this time, the molten bump formation materials 142a are shaped almost spherical as shown in FIG. 5C. Thereafter, electrodes 7 of a semiconductor element 1 are adjusted to coincide with the positions of the bump formation materials 142a in a state in which the bump formation materials 142a are melted, as shown in FIG. 5D. The bump formation materials 142a and the electrodes 7 are then bonded together as shown in FIG. 5E, and solder bumps 142b are obtained.
After the solder bumps 142b are formed, the base 143 is removed as shown in FIG. 5F, and a metallic plate 146 is pressed against the solder bumps 142b. As a result, the surfaces of the solder bumps 142b are flattened as shown in FIG. 5G, in other words, the solder bumps 142b undergoes coining, and a flat part 142c is formed for each of the solder bumps. Thereafter, the solder bumps 142b are bonded to lands 5 of a package substrate 2 as shown in FIG. 5H.
However, the following problems reside in the bump transfer plates and the semiconductor devices.
In general, the concave portions 8 are formed on the surface of the semiconductor element 1 as shown in FIG. 4A and FIG. 5D. Therefore, when the solder bumps 122 are transferred to the electrodes 7 of the semiconductor element 1 by using the bump transfer plate 121 shown in FIG. 1, gaps 120 are generated in the concave portions 8, as shown in FIG. 4B, in transferring the solder bumps 122 to the electrodes 7 if the tops of the solder bumps 122 are flat. Therefore, voids 127 exist, as shown in FIG. 4D, in the solder bump 122 obtained after the transfer, because of air remaining in the gaps 120. The strength of a junction between the solder bump 122 and the electrode 7 is weakened if the void 127 thus exists in the solder bump 122. Additionally, in a heat treatment process or the like required in, for example, a process of mounting the semiconductor element 1 and the package substrate 2, the possibility that the void 127 expands, and breakage is caused in the junction will increase. As a result, there is a problem in that yield decreases, and productivity decreases.
Especially, in the conventional method of manufacturing the bump transfer plate disclosed in Japanese Laid-open Patent Publication No. Hei 9-148330, the bump formation material 142a is bonded to the electrode 7 while being melted, as mentioned above. At this time, the bump formation material 142a is bonded to the electrode 7, in most cases, in a state in which the material 142a is shaped almost spherical because of melting. It is, however, difficult to cause the molten bump formation material 142a to coincide with the position of the electrode 7 of the semiconductor element 1 so as to form the solder bump 142b. Even if it is possible, another special manufacturing device must be newly used. If another manufacturing device is used, the labor required for the manufacturing process increases, and, at the same time, manufacturing costs increase, thus causing a sudden rise in product costs.
In addition, the resist layer 144 on the base 143 is made of, for example, a photosensitive polyimide film, and is formed with a spin coater. When the resist layer 144 is formed with the spin coater, the thickness of the resist layer 144 to be formed is about 20-30 xcexcm. On the other hand, with the recent miniaturization of a semiconductor device, so-called solder bump pitch narrowing (i.e., narrowing the distance (pitch) between adjoining solder bumps) has advanced. However, even if the pitch between the solder bumps 142b to be transferred to the semiconductor element 1 is narrowed by the use of the bump transfer plate 141, it is difficult to increase the thickness of the resist layer 144 more than the thickness (about 30 xcexcm) mentioned above because of the spin coater method. Therefore, the adjoining bumps cannot be divided sufficiently, and are connected to each other when the solder bumps are formed and transferred. As a result, work yields decrease in the formation and the transfer of the solder bumps by plating.
Additionally, after the solder bump 142b is formed on the electrode 7, it is bonded to the package substrate 2. At this time, the solder bump 142b is bonded to the land 5 disposed on the package substrate 2, as mentioned above, and the solder bump 142b undergoes coining in accordance with the kind of package substrate to be bonded or the size of the land 5. This is a step to reliably bond the surface of the solder bump 142b and the package substrate 2 together. The labor required in the manufacturing process depending on this step is also increased.
Additionally, with the recent miniaturization of the semiconductor devices, there is a tendency for the bump diameter also to become smaller. Therefore, there is another problem in that it is difficult to control the thickness of a minute bump during the coining.
It is an object of the present invention to provide a bump transfer plate and a manufacturing method thereof in which the productivity of a semiconductor device can be improved, and provide a semiconductor device a manufacturing method thereof that have high yields and high productivity.
According to one aspect of the present invention, a bump transfer plate comprises a base and a solder bump formed on the base. A top portion of the solder bump inclines from a central part thereof to a peripheral part thereof.
According to the bump transfer plate, since the solder bump is formed on the base, and the top portion of the solder bump inclines from the central part thereof to the peripheral part thereof, an electrode and the solder bump can be bonded together without generating any gap between the electrode and the solder bump when the solder bump is transferred to the electrode provided on the semiconductor element or the package substrate by the use of the bump transfer plate. Accordingly, the generation of voids is reduced, and the solder bump is prevented from breaking because of the expansion of the voids in the later process, which has conventionally occurred. As a result, productivity is improved and, at the same time, the nonuniformity in size of the solder bumps can be restrained which is caused by the voids.
In addition, since a contact surface of the solder bump with the base is made flat, the top portion of the solder bump is not required to undergo coining before the solder bump is bonded to another substrate, for example. Therefore, the labor required for manufacturing can be reduced.
If the base is made of aluminum, the solder bump easily peels off the base when the solder bump is transferred to the electrode because an oxide film is easily formed when the surface thereof comes in contact with air. As a result, the working efficiency of the transfer is improved.
If the base is made of stainless steel, the solder bump easily peels off the base when the solder bump is transferred because an oxide film is formed on the surface thereof. Therefore, since there is no need to newly form an oxide film for easily peeling the solder bump, the working efficiency of the transfer is improved.
According to another aspect of the present invention, a first method of manufacturing a bump transfer plate includes a step of forming a photo resist layer on a base. The photo resist layer has a hole at a region where a solder bump is intended to be formed. The method further includes steps of stacking a bump formation material into the hole and on the photo resist layer and removing the photo resist layer to form a solder bump.
A second method of manufacturing a bump transfer plate includes a step of forming a photo resist layer on a base. The photo resist layer has a hole at a region where a solder bump is intended to be formed. The method further includes steps of stacking a bump formation material into the hole and on the photo resist layer, applying flux onto a surface of the bump formation material, heating said bump formation material and said flux, and removing the flux to form a solder bump.
According to these manufacturing methods, there can be easily obtained a solder bump that is shaped to incline from the center thereof to the periphery thereof and whose top portion is rounded.
A third method of manufacturing a bump transfer plate includes a step of burying a solder paste in a hollow formed in a bump formation substrate. The deepest part of the hollow is rounded. The method further includes steps of overlapping a base on a surface of said bump formation substrate where said hollow is formed, and heating said solder paste and said base to form a solder bump.
According to this manufacturing method, there can be easily obtained a solder bump that is shaped to incline from the center thereof to the periphery thereof and whose top portion is rounded. In addition, a solder bump can be easily obtained that is variously shaped for various uses by adjusting the shape of the hollow.
According to another aspect of the present invention, a first method of manufacturing a semiconductor device includes a step of bonding an electrode provided to a semiconductor element and the solder bump together subsequent to the steps of one of the aforementioned bump transfer plate manufacturing methods.
According to the manufacturing method, the electrode and the solder bump can be bonded together without generating any gap between the electrode and the solder bump when the solder bump is transferred to the electrode. Accordingly, the generation of voids is reduced, and the solder bump is prevented from breaking due to expansion of the voids caused by heat treatment in the later process. As a result, productivity is improved and, at the same time, fluctuation in size of the solder bumps can be restrained which is caused by the voids. In addition, if a contact surface of the solder bump with the base is made flat, the top portion of the solder bump is not required to undergo coining before the solder bump is bonded to another substrate or the like. Therefore, the labor required for manufacturing can be reduced.
According to another aspect of the present invention, a second method of manufacturing a semiconductor device includes a step of bonding an electrode provided to a package substrate and the solder bump together subsequent to the steps of one of the aforementioned bump transfer plate manufacturing methods.
According to the manufacturing method, the electrode and the solder bump can be bonded together without generating any gap between the electrode and the solder bump when the solder bump is transferred to the electrode. Accordingly, the generation of voids is reduced, and the solder bump is prevented from breaking due to expansion of the voids caused by heat treatment in the later process. As a result, productivity is improved and, at the same time, fluctuation in size of the solder bumps can be restrained which is caused by the voids.
According to another aspect of the present invention, a semiconductor device is manufactured by one of the aforementioned methods. The ratio of voids existing in the solder bump is 10% or less per unit sectional area of said solder bump.
If the ratio of voids existing in a solder bump exceeds 30% of the unit sectional area of the solder bump, the strength of the junction between the solder bump and an electrode decreases. Additionally, the possibility will increase that the voids expand and the junction is broken in heat treatment during the manufacturing process. Therefore, yields might decrease when the void ratio exceeds 30%.
In contrast, in the semiconductor device according to the present invention, the ratio of voids existing in the solder bump is 10% or less of the unit sectional area of the solder bump, and therefore the junction between the solder bump and the electrode is prevented from cracking or breaking due to expansion of the voids. Therefore, the yield is high, and the reliability is also high.